1. Field of the Invention
The present invention relates to a receiver of the diversity system and, particularly, to a diversity receiver having a fault detecting function for reducing degradation of a receiving signal quality due to fault.
2. Description of the Related Art
A conventional diversity receiver of this kind has been used to improve degradation of error rate in a receiver of a radio communication system due to fading, as disclosed in, for example, Japanese Patent Application Laid-open No. Hei 6-204925.
FIG. 5 is a block diagram showing one of examples of conventional diversity receivers. As shown in FIG. 5, the diversity receiver includes a first receiving circuit 1, a second receiving circuit 2, a switch 3 and a receiving level detection circuit 4.
The first receiving circuit 1 is input with a first receiving signal 21 and outputs a first receiving data 23 and a first receiving level data 25 indicative of an electric field intensity of the first receiving signal 21. On the other hand, the second receiving circuit 2 is input with a second receiving signal 22 and outputs a second receiving data 24 and a second receiving level data 26 indicative of an electric field intensity of the second receiving signal 22. It is noted that the first receiving signal 21 and the second receiving signal 22 are the same signal, but received by a different antenna located in a different position respectively.
Further, the receiving level judge circuit 4 is input with the first receiving level data 25 and the second receiving level data 26, compares them and judges one of them whose electric field intensity is higher than the other and outputs the judging result as a level judge signal 30. The switch 3 has inputs supplied with the first receiving data 23 and the second receiving data 24 and outputs one of the receiving data 23 and 24 whose electric field intensity is higher according to the level judge signal 30 from the receiving level judge circuit 4.
In the foregoing conventional diversity receiver, when the receiving signal is weak and its signal level is low, there may be a case where the receiving level data of a fault receiving circuit, which does not output receiving data properly, becomes the same as that of a normal receiving circuit. Therefore, there may be a case where, although the receiving data of the normal receiving circuit is to be selected, the receiving data of the fault receiving circuit is selected and thus there is a defect that the communication quality is degraded when the receiving level is low and one of the receiving circuits is faulty.